The object of the present invention is a process which permits improved covering of the frame of an article of plastics material which is internally reinforced and concerns reinforced plastics articles thus obtained.
For various applications, and especially to form crates to hold heavy loads or to form handling pallets, the conventional plastics materials, even those of good quality, have insufficient rigidity and strength under load. One solution which has been adopted consists in reinforcing these articles by means of internal framework members.
Thus, in the earlier French patent filed in the name of the Applicants, No. 7917420 dated June 29th, 1979, there are described articles of plastics material internally reinforced by means of wooden frame members. The processs described in this earlier application is equally applicable if the frame members are of a different nature, for example of metal.
The manufacturing problem which arises is the moulding of the plastics materials onto the frame. A priori, this could not cause manufacturing problems if the plastics material were not subject to any substantial shrinkage during cooling after having been moulded onto the frame. Now, the shock-resistant plastics materials which are used for such articles, for example high density polyethylene, are highly subject to cracking under stress, or have other disadvantages. Consequently, it has been proposed to coat the framework by means other than a single over-moulding. Thus, according to the previously-mentioned patent, open channels are formed in the shock-resistant plastics material in which the frame members are positioned. After this, the opening in the channel is closed by moulding, onto the framework and a portion of the external wall of the channel, a material which is not susceptible to cracking under strain. As the latter cannot be sufficiently welded to the exterior walls of the channel, there is obtained over and above the shrinkage grip, a mechanical connection between the frame, channels, and over-moulded article by providing grooved throats in the frame, and facing orifices in the channels, so as to obtain a bond between the added piece and the framework via the channels which surround it thanks to connecting and locking pins.